The effects of various DNA damaging agents were compared in human skin fibroblasts and human bronchial epithelial and fibroblast cells. The three cell types exhibited the same 1) rate of repair of DNA single strand breaks (SSB) after X-ray, 2) rate of excision repair after UV-radiation, and 3) level of SSB after exposure to 7,12-dimethylbenz(a)anthracene, benzo(a)pyrene diol expoxide (BPDE), and N-methyl-N'-nitro-N-nitrosoguanidine. DNA-protein crosslinks (DPC) induced by formaldehyde were rapidly removed in all cell types. Low concentrations of formaldehyde were rapidly removed in all cell types. Low concentrations of formaldehyde inhibited rejoining of X-ray induced SSB and synergistically potentiated X-ray induced toxicity in bronchial cells. Formaldehyde did not have any effect on unscheduled DNA synthesis. Repair replication was more than 2-fold higher in epithelial than in fibroblast cells after BPDE treatment. Asbestos and nickel did not induce any DNA damage and did not affect repair of damage induced by BPDE or UV-radiation.